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Zinc oxide main processes

Number of visits: Date:2011-07-28 15:23

Zinc oxide main processes: Indirect (French) process: Metallic zinc is melted in a graphite crucible and vaporized at temperatures above 907 °C (typically around 1000 °C). Zinc vapor instantaneously reacts with the oxygen in the air to give ZnO, accompanied by a drop in its temperature and bright luminescence. Zinc oxide particles are transported into a cooling duct and collected in a bag house. This indirect method was popularized by LeClaire (France) in 1844 and therefore is commonly known as the French process. Its product normally consists of agglomerated zinc oxide particles with an average size of 0.1 to a few micrometers. By weight, most of the world's zinc oxide is manufactured via French process. Major applications involve industries related to rubber, varistors, sunscreens, paints, healthcare, and poultry nutrients. Recent developments involve acicular nanostructures (rods, wires, tripods, tetrapods, plates) synthesized using a modified French process known as catalyst-free combust-oxidized mesh (CFCOM) process. Acicular nanostructures usually have micrometre-length nanorods with nanometric diameters (below 100 nm). Direct (American) process:In the direct process, the starting material is various contaminated zinc composites, such as zinc ores or smelter by-products. It is reduced by heating with a carbon additive (e.g. anthracite) to produce zinc vapor, which is then oxidized as in the indirect process. Because of the lower purity of the source material, the final product is also of lower quality in the direct process as compared to the indirect one. Wet chemical process:Wet chemical processes start with purified zinc solutions, from which zinc carbonate or zinc hydroxide is precipitated. It is then filtered, washed, dried and calcined at temperatures ~800 °C.

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